Preparation And Properties Of Heteroatom Doped Multicolor Fluorescent Carbon Dots

Fluorescent carbon dots(CDs)are a new type of fluorescent nanomaterials.Due to the small size of CDs,they are generally smaller than 10 nm,making them have a specific quantum confinement effect and have good fluorescence properties and biocompatibility.Meanwhile,Fluorescent CDs overcome the shortcoming of high toxicity of traditional quantum dots.Therefore,fluorescent CDs have great application potential in biological imaging,chemical sensing,photocatalysis and other related fields.Improving the optical properties of CDs by doping heteroatoms proved to be an effective way in the preparation of CDs.This dissertation focuses on the preparation of CDs with different emission wavelengths by doping with non-metallic elements and improves the fluorescence properties.The specific work is as follows:1 Commercial carbon black was used as a carbon source.Oxygen-doped blue fluorescent CDs(O-CDs)were obtained by physical extraction.The fluorescence emission wavelength of O-CDs showed excitation-dependent properties.The maximum emission wavelength was 400 nm.The extracted O-CDs were characterized by transmission electron microscopy(TEM).The results showed that the average diameter of O-CDs was 2.39 nm.The results of FT-IR and XPS showed that there were almost no hydrophilic groups on the surface of O-CDs,mainly carbon and oxygen.2 Nitrogen-sulfur doped green fluorescent CDs(N,S-CDs)with high fluorescence quantum yield(QY)were synthesized by hydrothermal method using m-phenylenediamine and mercaptosuccinic acid as precursors.The QY was as high as 66.84 %.Since N,S-CDs had a good response to solution pH,N,S-CDs were used for pH sensing.The TEM results showed that the N,S-CDs were spherical or spheroidal structures with uniform dispersion.The average size of N,S-CDs was 2.44 nm.The FT-IR and XPS analysis showed that N and S elements were successfully doped into CDs.There were free amino and thiol groups on the surface of CDs.As a pH switch,fluorescence intensity of N,S-CDs was enhanced under acidic conditions,weakened under alkaline conditions,and could be recycled.3 On the basis of the previous work,only o-phenylenediamine was used as a precursor to provide nitrogen source.Nitrogen-doped red fluorescent CDs(N-CDs)were synthesized by solid-phase reaction.The maximum excitation wavelength of N-CDs was 537 nm,the maximum emission wavelength was 600 nm.Due to the maximum excitation wavelength of N-CDs was in the visible range,which means visible light can be the excitation light.We successfully excited the N-CDs with the flashlight on the phone and also got the bright red fluorescence.TEM results showed that N-CDs had good dispersibility with an average size of 2.59 nm.It was proved by FT-IR and XPS analysis that N element was successfully doped into CDs.At the same time,the oxygen content was very low.